We will investigate the genetic basis of behavioral and morphological traits in two species of Drosophila: D. silvestris and D. heteroneura. These two species have diverged to a great extent in their behavior and morphology event though they share a close genetic relationship and habitat. Our previous research indicates theat the species differ in the intensity and form of aggressive interactions. Hybrids between the two species display a mixture of behaviors of the two parental species. Some of the aggressive behaviors display dominant genetic expression due to a few genes or a threshold expression of many genes. in other aggressive behaviors hybrids display an intermediate expression which may be due to many genes or an additive effect of a few genes. Courtship behaviors have diverged to such an extent that there is an asymmetry of mating between the two species with D. heteroneura males mating more readily with D. silvestris females than vice versa. However, the hybrids readily mate with both species indicating a non-additive inheritance for this behavior. We will identify quantitative trait loci (QTL) for differences between these two species using a backcross breeding design. From this breeding design we will develop a molecular linkage map using AFLP molecular techniques. We will then identify candidate QTL for aggressive and courtship behaviors and morphological traits and examine the QTL for physical linkage and pleiotropy among the various traits The identification of specific QTL and the genetic properties of the QTL will further our understanding of the genetic basis of behavior and morphology.